(OLE Control EXtension) A component software technology from Microsoft that enables a Windows program to add functionality by calling ready-made components. Generally called "OLE controls" or "OLE custom controls," they appear to the end user as just another part of the program.

OCXs are Microsoft's second-generation component architecture. Unlike first-generation 16-bit Visual Basic controls (VBXs), which were only written in Visual Basic, OCXs can be written in several languages and come in 16-bit and 32-bit versions. OCXs were renamed ActiveX controls and continue to use the .OCX file extension. See VBX and ActiveX control.